The impact of age at enrollment on subsequent school performance remains unclear. Some have argued that when parents delay putting their children in school it allows their children to gain experience, mature, prepare more for the school experience, and consequently perform better. Others argue the opposite - that school performance of children is enhanced when they enter school at younger ages. It is argued that children who enter earlier perform better because they are stimulated more and interact in a more enriched environment than they would have had the children remained at home. The empirical literature on this issue is unsettled. Moreover, it is difficult to interpret empirical results from many studies that do not consider that a parent's decision about when to enroll a child in school is likely to be determined in part by that child's ability. To the extent that parents enroll high ability children at younger ages, early enrollment will be correlated with high performance but this will not be a causal relationship. Consequently it is important to account for this potential selection bias. . There is ample empirical evidence that points to a strong association between educational attainment, economic well-being and health. Because ultimate educational attainment is built up from early foundations, it is critical to understand whether and how early educational performance can be enhanced, especially for children from groups that are traditionally .at risk to drop out of school. We will investigate the relationship between school performance and age at first enrollment, accounting for three types of selection bias - selective labor force participation of mothers, enrollment in pre-school programs, and the age a parent enrolls a child in first grade. To account for the potential selection bias found in patterns of enrollment ages we apply an instrumental variables (IV) technique using variation across states and over time in laws that specify the maximum age children may be before they must enroll in school and the minimum age children may enroll in public school. We take advantage of a sample of siblings who faced different compulsory schooling laws, either because of their birth order or because their parents moved across state lines. [unreadable] [unreadable] [unreadable]